Cooking appliance door with an inner borosilicate glass window pane and cooking appliance with said door

ABSTRACT

The cooking appliance door has a borosilicate glass inner window pane, on which a paint layer and an infrared-reflecting layer are applied. The paint layer is high-temperature-resistant non-enamel paint with an organic or inorganic binder. In order to provide especially good adherence and high scratch resistance for the paint layer, the paint layer is applied directly on one side of the inner window pane and the infrared-reflecting layer is applied on and over this paint layer. A cooking appliance with this cooking appliance door is also part of this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a cooking appliance door with an inner windowpane comprising a borosilicate glass, on which a paint layer made from ahigh-temperature-resistant non-enamel paint with an organic or inorganicbinder and an infrared-reflecting layer are applied. The invention alsorelates to a cooking appliance with this sort of door.

2. Description of the Related Art

A household cooking appliance, especially an oven, has a cooking chamberor compartment with an opening, which is closable by a cooking appliancedoor with an observation or viewing window. Cooking appliances with adoor that is completely glass are known. A baking oven with an ovenmuffle acting as cooking compartment is a typical currently knownhousehold appliance. This sort of baking oven has been equipped to alarge extent with a pyrolytic self-cleaning means, by which cookingresidues are decomposed to ash at pyrolysis temperatures above 500° C.

The typical household cooking appliance door and thus its viewing windowis of course heated during operation due to the comparatively hightemperatures in the cooking appliance. An entirely glass appliance door,which typically comprises a glass pane packet, is also heated duringoperation. The same is true to a special extent during the pyrolysisoccurring at extremely high temperatures in pyrolyzing baking ovens.High-quality glass is used for door panels of cooking appliances becauseof this high heat load. This is particularly true for the viewingwindows or full glass doors for cooking appliances and baking ovens withpyrolytic self-cleaning means. A pre-stressed borosilicate glass is thusused for the inner window pane that is closest to the oven muffle. Thissort of glass is characterized by a special resistance to hightemperatures.

In order to keep the temperature on the outer side of the viewing windowor full glass door of the cooking appliance as small as possible toreduce the danger of burns and other injuries due to contact with theouter surface of the viewing window, the viewing window is provided witha coating that reflects heat into the interior of the cookingcompartment, i.e. an infrared-reflecting coating. An observation windowdescribed in U.S. Pat. No. 4,898,147 has an inner window pane made fromborosilicate glass with an infrared-reflecting multilayer coating andnoble gas layer between the inner and outer window panes, in order toreduce the heat transferred. A so-called “cold door” for apyrolysis-baking oven is thus provided by means of these features. This“cold door” is defined by GIFAM DOC 266/01 by stating an upper limitingtemperature, which the contacting surface of the door can have, when theoutside temperature is 23° C. and the temperature in the cookingcompartment is about 500° C. (with glass, less than 70° C.).

Furthermore it is known to provide the borosilicate glass inner windowpane with printing made from enamel paint, comprising special writing(letters, words) and symbols, especially usage hints for the operators,particularly which indicate different cooking programs. This printedinformation can be located on the side of the inner window pane facingthe door interior and also on the side facing the cooking compartment,as described in DE 100 07 923 C1. DE 101 43 925 A1 discloses a suitableborosilicate inner window pane for a cooking appliance door printed withenamel paint.

Conventional enamel paints melt or fuse with the glass surface duringburning on the borosilicate inner window pane. Stresses are developed inthe glass window pane due to the differing thermal expansion propertiesof the glass window pane and the printing with the enamel paint. Thesestresses occur in connection with interactions (ion exchange) betweenthe enamel paint, a glass flux-based print ink and the borosilicateglass. Because of that the impact resistance of the glass window pane isdegraded for impacts on the side facing away from the printedinformation. For that reason the above-mentioned DE 100 07 923 C1suggests that the color printing printed with the enamel paint should beapplied to the outside of the inner window pane facing or turned towardthe interior of the cooking compartment. Since the current enamel paintsare not heavy-metal-free, especially not lead-free, there is a dangerthe heavy metals, especially lead, could be volatilized in the cookingcompartment at higher operating temperatures because of the colorprinting on the exposed side in direct contact with the cookingcompartment. Furthermore the enamel paint coating has a rough,unpleasing surface.

There is no enamel print or enamel for printing currently known forborosilicate glass, which (1) is heavy-metal-free, (2) has a smoothaesthetically pleasing surface and (3) maintains the impact resistanceof the borosilicate glass pane, when the impacts occur on the sidefacing away or opposite from the printing. As a result, non-enamel paintwith organic (e.g. silicones or fluoropolymers) or inorganic (e.g. waterglass; sol-gel binders) binders was develop, which in contrast to theconventional enamel paint is not bonded with the glass surface bymelting. These non-ceramic paints are described in the old Patentapplication DE 103 13 630, whose subject matter is incorporated hereinby explicit reference thereto.

This paint is only a SiO₂-based paint with carbon particles, which arecoated or enveloped by SiO₂, as pigment, as is described in DE 195 25658 C1.

Up to now the color printing on inner window panes of borosilicateviewing windows with infrared-reflecting coatings provided by theabove-described non-enamel paints has been applied directly to theinfrared-reflecting coating. This leads to certain process uncertaintiesand unreliabilities, since the adherence of the paint developed fordirect application to borosilicate glass is not guaranteed on aninfrared-reflecting coating. The infrared-reflecting coating usuallycomprises a tin oxide material, which differs significantly from aborosilicate glass. Furthermore the above-described paint coating is notvery resistant to scratching.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a cooking appliancedoor of the above-described type with an inner window pane comprisingborosilicate glass, which has an infrared-reflecting coating andprinting, such that the printing reliably adheres to the window pane andresists scratching.

This object and others, which will be made more apparent hereinafter,are attained in a cooking appliance door with an inner window panecomprising a borosilicate glass, on which a paint layer, which comprisesa high-temperature-resistant non-enamel paint with an organic orinorganic binder, and an infrared-reflecting layer are applied.

According to the invention surprisingly the paint layer is applieddirectly on one side of the inner window pane and theinfrared-reflecting layer is applied on and/or over this paint layer.

The present invention also includes a cooking appliance with theabove-described cooking appliance door according to the invention.

Because of the critical feature of the invention, i.e. the applicationof infrared-reflecting layer after applying the color printing or paintlayer to the inner window pane, one very advantageously obtains aresistant color printing on the inner window pane of borosilicate glass.Besides greater adherence of the paint layer on the glass substrate thecolor printing is also scratch-resistant, since the infrared-reflectinglayer is very hard and thus mechanically protects the printedinformation provided by the non-enamel paint. Furthermore use of thenon-enamel paint in this manner also maintains the impact strength forimpacts occurring on the side of the inner window pane opposite from theside bearing the printing. The printing also can be provided on the sideof the inner window pane facing away from or opposite from the cookingcompartment. In that case there are no interactions between the coatingand the cooking compartment.

Of course the color printing can also be provided on the side of theinner window pane closest to or facing the cooking compartment,especially with the infrared-reflecting coating covering the colorprinting. Thus the occurrence of printing with paint portions in thecooking compartment is at least reduced.

DE 101 62 220 A1 discloses a two-layer coating on a glass pane for acooking appliance door. This two-layer coating comprises a first dark,especially black colored, heat-radiating layer and above it a secondwhite colored heat reflecting layer. The second layer should reflect asubstantial part of the radiated heat back into the oven. In contrastheat, which reaches the glass pane, should be radiated away by the firstdark layer.

DE 101 62 220 A1 does not provide any hint or suggestion of a paintcoating made from non-enamel paint or a solution of the associatedadherence problems due to the foregoing problems.

BRIEF DESCRIPTION OF THE DRAWING

The objects, features and advantages of the invention will now beillustrated in more detail with the aid of the following description ofthe preferred embodiment, with reference to the following figures, inwhich

FIG. 1 is a diagrammatic cutaway cross-sectional view through an innerwindow pane of an observation window of a cooking appliance door or acompletely glass door, especially a cooking oven door; and

FIG. 2 is a schematic cross-sectional view through one embodiment of acooking appliance including a cooking appliance door according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

This inner window pane 1 is exposed to the highest temperatures becauseit is immediately adjacent to the hot oven muffle or cooking compartment30 (FIG. 2) during operation of the cooking appliance 10. This isespecially true during pyrolytic self-cleaning, in which temperatures ofover 500° C. are present in the cooking compartment 30. Because of thisreason the inner window pane 1 of the cooking appliance door 20 is madefrom borosilicate glass, preferably from a pre-stressed borosilicateglass, which has a high resistance to these high temperatures and asmall thermal expansion coefficient. The color printing or paint layer 2is printed on one side of the inner window pane, which is an interiorside as shown in this embodiment. The color printing or paint layer 2can form a colored surface or also letters or symbols, which provide ahint or suggestion for the operator, especially of different cookingprograms that the cooking appliance can perform. The color printing orpaint layer 2 is made from the above-described non-enamel paint, whichis applied directly to the inner surface of the borosilicate glass ofthe inner window pane by a printing process, especially a screenprinting process and burned in after that. The layer thickness ispreferably in a range of 10 to 15 μm. The printing preferably occurs ina dot matrix or pattern.

Subsequently an infrared-reflecting coating 3 is applied to the colorprinting or paint layer 2, for example by a hot spraying process. Thiscoating 3 typically contains tin oxide as “effective ingredient” and isusually formed in a know way, e.g. in regard to coating thickness, etc.These IR-reflecting coatings are especially known for heat-resistantglazing (e.g. K-GLAS® or OPTIFLOAT® mirror glass), and for example aredescribed in DE 198 25 437 A1. Since the infrared-reflecting layer 3 isvery hard, the scratch-resistance of the color printing 2 is high, andthe adherence of the color printing directly on the glass surface isvery high.

The preferred embodiment shown in the sole Figure has only a singleIR-reflecting coating and a single color printing or paint layer. It isunderstandable however that another embodiment could have more than oneof each of these layers.

FIG. 2 shows a cooking appliance 10 including a simplifiedrepresentation of a cooking appliance door 20 according to theinvention. The cooking appliance door 20 includes an inner window pane 1made of borosilicate glass. As explained above, the inner window pane 1is first provided with color printing or a paint layer 2 on its surfaceclosest to or facing the cooking compartment 30. Then aninfrared-reflecting coating 3 is provided on the inner surface of theinner window pane 1 by a hot spraying method, so that the coating 3completely covers the color printing or paint layer 2.

The disclosure in German Patent Application 103 44 442.4-16 of Sep. 25,2003 is incorporated here by reference. This German Patent Applicationdescribes the invention described hereinabove and claimed in the claimsappended hereinbelow and provides the basis for a claim of priority forthe instant invention under 35 U.S.C. 119.

While the invention has been illustrated and described as embodied in acooking appliance door with an inner window pane made of borosilicateglass and a cooking appliance containing that door, it is not intendedto be limited to the details shown, since various modifications andchanges may be made without departing in any way from the spirit of thepresent invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior this invention.

1. A cooking appliance door comprising an inner window pane (1), saidinner window pane comprising borosilicate glass; at least one paintlayer (2) applied directly to a surface on one side of said inner windowpane, wherein said at least one paint layer (2) comprises ahigh-temperature-resistant non-enamel paint with an organic or inorganicbinder; and at least one infrared-reflecting layer (3) applied on saidat least one paint layer (2) on said one side of the inner window pane.2. The cooking appliance as defined in claim 1, wherein said at leastone paint layer (2) has a thickness of from 10 to 15 μm.
 3. The cookingappliance as defined in claim 1 or 2, wherein said at least one paintlayer (2) is printed on the inner window pane (1).
 4. The cookingappliance as defined in claim 1, wherein said at least oneinfrared-reflecting layer (3) contains tin oxide.
 5. The cookingappliance as defined in claim 1 or 4, wherein said at least oneinfrared-reflecting layer (3) is applied to the at least one paint layer(2) by a hot spraying process.
 6. A cooking appliance (10) comprising acooking compartment (30) with an opening for placing cooking materialsin the cooking compartment (30) and a cooking appliance door (20) forclosing said opening; wherein said cooking appliance door (20) comprisesan inner window pane (1) made of a borosilicate glass, at least onepaint layer (2) applied directly to a surface on one side of said innerwindow pane, said at least one paint layer (2) comprising ahigh-temperature-resistant non-enamel paint with an organic or inorganicbinder and at least one infrared-reflecting layer (3) applied on said atleast one paint layer (2) on said one side of the inner window pane. 7.The cooking appliance as defined in claim 6, wherein said at least onepaint layer (2) has a thickness of from 10 to 15 μm.
 8. The cookingappliance as defined in claim 6, wherein said at least oneinfrared-reflecting layer (3) contains tin oxide.